Field of the Invention
The present invention relates to exhaust-control devices for circuit-interrupting devices such as fuses, and more particularly to an exhaust-control device that utilizes a first heat-absorbing medium to cool the exhaust so as to avoid any significant melting of or deleterious effects to a second heat-absorbing medium through which the exhaust passes after passing through the first heat-absorbing medium.
Related Art
During operation of a circuit-interrupting device such as a fuse, hot arc products and gases are discharged which will be generally referred to as "exhaust gases" hereinafter. In many applications, it is desirable to prevent discharge of these exhaust gases into the atmosphere or local environment. Specifically, it is desirable to reduce the noise level during operation and to absorb substantially all of the energy of the exhaust gases, thus preventing the hot arc products and metallic vapors in the exhaust gases from entering the environment. Exhaust-control devices of the type that perform these functions are disclosed in U.S. Pat. Nos. 3,719,912, 3,909,570, 3,965,452, 4,001,750, and 4,103,129. This type of exhaust-control device reduces the sound level and the gas discharge without significantly interfering with the intended circuit-interrupting function of the fuse or device. Further, this type of exhaust-control device, unlike non-vented devices, does not create unsuitably high back pressures to the circuit-interrupting device which might cause undesirable effects, including higher pressures and operating temperatures, longer arcing time, and higher operating energies that must be dissipated.
It is also desirable that the exhaust-control device be as small and light-weight as possible, while retaining efficiency of operation and being capable of functioning repeatedly without loss of effectiveness.
However, if a heat-absorbing medium that has a melting point below the highest temperature of the exhaust gases is utilized, as is the case for example with woven copper mesh or screen, sufficient heat-absorbing medium must be provided so that the exhaust-control device is capable of functioning after a portion of the heat-absorbing medium is melted. This, of course, requires a larger quantity and volume of heat-absorbing medium than would be required if the heat-absorbing medium were not melted at all by the hot exhaust gases. If a heat-absorbing medium that has a higher melting point is utilized, for example ceramic pellets or balls, the ceramic medium is not readily available in shapes that optimize the flow of exhaust gases or the transfer of heat into the ceramic medium. Additionally, the melting temperature of the ceramic medium is not high enough to totally eliminate melting at the temperature of the exhaust gases. Accordingly, the ceramic medium also tends to plug up when the circuit-interrupting device interrupts high currents. The relatively low thermal conductivity and low specific heat at lower temperatures also are drawbacks of a ceramic medium.